Devices of the kind mentioned above are to a great extent used for instance in lifting tables, which in the initial position, before initiation of the lifting movement, should have a very low height, i.e. wherein lifting arms and the force applying means included in the lifting table preferably should be oriented generally parallel to each other on the ground. In order that it may be possible to initiate a lifting movement in this case, it is necessary that the connection of the force applying means to the lifting arms is designed especially with regard to this. Examples thereof are the devices disclosed in the Swedish specifications 8304655-7, 8501852-1 and 8602983-2, the U.S. Pat. Nos. 2,862,689 and 2,937,852 as well as German patent specification 17 56 270. In all these devices the lifting movement is initiated by the means that the end of the power applying means forces apart obliquely oriented glide surfaces arranged on each lifting arm, for instance by means of a roller arranged at the end of the force applying means. The force applying means here generally comprise hydraulic cylinders. These previously known constructions function in an excellent way, but, since the glide surfaces are subjected to comparatively large forces from the force applying means when the lifting movement is initiated, these glide surfaces may be subjected to wear and/or deformation, which may have detrimental effect on their function. The construction with rollers and slide surfaces is comparatively expensive and complicated. In addition to this, comparatively high hydraulic pressures generally are necessary due to the specific geometry which is a result of the resulting, comparatively short, effective length of the arms of leverage, which results in that high demands have to be made on the hydraulic equipment.
U.S. Pat. No. 3,991,857 furthermore discloses a lifting device of the kind mentioned in the introduction, in which a roller indirectly is guided and forced in between two surfaces obliquely oriented relative to each other (one oblique surface being arranged on one of the lifting arms and one being the base plate) by means of a complicated system of control plates and abutments guiding the movements of the roller. This device in principle functions in a similar way as the devices described above and suffers generally from the same disadvantage.
U.S. Pat. No. 2,899,172 finally discloses a lifting device of the kind mentioned in the introduction which is constructed and intended for trucks. In this device the lifting movement is initiated by means of a lever acting against the truck frame. This construction thus is limited to a use in connection with stable frames of the kind used in truck frames.